1. Field of the Invention
Embodiments of the present invention generally relate to the field of medical imaging and the field of radiography. More particularly, embodiments of the present invention relate to dual-energy scanners.
2. Description of the Prior Art
Dual-energy scanners may be single-source scanners periodically emitting radiations with two different energies typically of the order of 80 kV and 140 kV respectively, and switching very rapidly from one to the other (of the order of about a thousand switches per revolution of the scanner, and from about 0.5 to about 5 revolutions per second).
As these radiations with different energies are not transmitted or reflected in the same way by organic tissues, notable enrichment of the information obtained in the final image, and an increase in its resolution may be achieved.
As shown in the graph of FIG. 1, which represents the energies of the emitted radiations versus time, these scanners nevertheless require transition times (called Trise and Tfall in the figure) for switching from one energy to the other and vice versa, during which the energy is variable and distinct from the two “useful” energies E1 and E2 used for the imaging of a patient.
The emitted radiation doses during these transition times therefore only have a low interest for the image; furthermore, they provide an additional dose of radiations to the patient, whereas doses should be minimized in order not to be dangerous for the health of the patient.
Efforts have already been made for limiting the transition time between the useful energies, but there remains a phase during which the patient receives an unnecessary dose.
Furthermore, reducing the transition time complicates the structure of the electronic circuit used in the scanner and makes the latter heavier.
Therefore, there exists a need for a novel technique with which images may be produced from radiations with two different energies without these images being altered by additional radiations of non-useful energies, and in which the doses of non-useful radiations absorbed by the patient are limited.
Methods for applying sources of radiations have already been developed with which all or part of the radiations may be prevented from attaining a patient, in order to modulate the dose received by this patient.
To achieve this, radiation sources of the type comprising a source of electrons and a target, adapted so as to emit a flux of X-rays towards a patient or an area of the patient to be imaged when it receives a flux of electrons, are used.
The source further comprises a system for deflecting the flux of electrons, which modifies the path of the electron flux so that it attains another point of the target and the dose sent towards the patient is modified.
However, with such a device, it is only possible to achieve dose modulation, but not to mask certain energies at given time intervals; the obtained result is therefore not satisfactory.